Manufacturing processes of a field-effect transistor constituting an integrated circuit formed in a semiconductor region will be described with reference to FIG. 1, using an LDD (Lightly Doped Drain)-structure n-type field-effect transistor as an example.
At first, element isolation is carried out, for example, by an STI (Shallow Trench Isolation) method, thereby forming an element region 102 on the surface of a p-type (100) plane silicon 101 serving as a semiconductor substrate (FIG. 1(a)).
Pre-oxidation cleaning such as RCA cleaning is applied to the element region 102 (FIG. 1(b)) to remove organic compounds, particles, and metal impurities and, thereafter, dilute hydrofluoric acid treatment and then rinsing with pure water are performed to hydrogen-terminate 103 the element region 102 (FIG. 1(c)). After drying the wafer (FIG. 1(d)), a gate insulating film (SiO2) 104 is formed (FIG. 1(e)).
Then, boron is ion-implanted over the entire surface of the silicon 101 for controlling the threshold voltage (FIG. 1(f)).
Then, a polycrystalline silicon film is deposited over the entire surface of the silicon 101 and then patterned, thereby forming a gate electrode 105 of polycrystalline silicon on the gate insulating film 104 in the element region 102 (FIG. 1(g)).
Then, phosphorus is ion-implanted at a low concentration, thereby forming n− source and drain regions 106 that serve to relax high electric fields (FIG. 1(h)).
Then, a silicon oxide film (SiO2) is deposited over the entire surface of the silicon 101 by a CVD method or the like so as to cover the gate electrode 105 and then anisotropic etching is performed, thereby forming a side-wall insulating film 107 on the side walls of the gate electrode 105 (FIG. 1(i)).
Thereafter, n-type impurities such as arsenic are ion-implanted at a high concentration, thereby forming n+ source and drain regions 108 (FIG. 1(j)).
In Patent Document 1, the present inventors have previously pointed out that the hydrogen termination is deteriorated in a cleaning process, and proposed a technique for solving it.
In the case of the field-effect transistor forming method shown in FIG. 1, the process up to the formation of the gate insulating film 104 becomes discontinuous after the dilute hydrofluoric acid treatment to carry out the hydrogen termination 103. After drying the wafer, the wafer goes through stages of being placed in a carrier container, transferred to a gate oxidation apparatus, and subjected to the gate oxidation. In this case, after the drying up to the gate oxidation, the wafer is exposed to a CR (clean room) atmosphere. During this time, the terminated hydrogen 103 formed on the surface of the element region 102 is impaired with the lapse of time so that oxidation of the surface proceeds (FIG. 1(d)). A natural oxide film formed on the surface is nonuniformly formed over the element region 102 and, further, the density of the film itself is low, which thus becomes one cause for degrading the quality of the gate insulating film 104 formed thereafter.
The foregoing description is given using the n-type field-effect transistor as an example, but the same also applies to a semiconductor element such as a p-type field-effect transistor, a TFT, a CCD, or an IGBT.
In view of the problem described above, an attempt has been made to transfer a wafer in a vacuum or in an N2 atmosphere from the drying process after the dilute hydrofluoric acid treatment to the gate oxidation. However, it is known that organic compounds adhere to the surface of the element region 102 in the vacuum transfer and, also in the transfer in the N2 atmosphere, the hydrogen termination is impaired with an increase in exposure time and thus the growth of a natural oxide film cannot be completely suppressed.
On the other hand, Patent Document 1 only points out the deterioration of the hydrogen termination in the cleaning process, but does not disclose that the hydrogen termination is also deteriorated during the vacuum transfer.    Patent Document 1: Japanese Unexamined Patent Application Publication (JP-A) No. 2005-51141